Modular ventilation system simplifies retrofit at San Francisco landmark

The Fanwall Technology modular fan-cube system replaced a single, large air-handler fan, lowering costs and reducing energy use at the Transamerica Pyramid.

Information provided by Huntair.

01/19/2012

As integral to the San Francisco skyline as the Golden Gate Bridge and the Coit Tower, the Transamerica Pyramid has been recognized as an avant-garde building since the first cornerstone was laid in 1969. The iconic pyramid-shaped building, owned by AEGON since 1999, is part of the larger Pyramid Center complex that encompasses an entire city block in the Financial District. Architects William Pereira and Assocs. chose the pyramid shape not just for its unusual look, but also to meet a specific need: A pyramid casts a smaller shadow than a conventional high-rise building does, allowing more light to filter to the streets below. At the time, that met the requirements of a special “shadow ordinance” in San Francisco. The building’s cutting-edge tradition continues today: upgrades and retrofits have earned the building U.S. Green Building Council LEED Gold certification, and a recent upgrade to one section of the building’s HVAC system is also inventive.

The aging air-handler fans serving floors 1 to 18 of the building required continual maintenance because of their age. Building management sought a replacement that would cause minimal disruption to tenants, simplify and reduce costs for installation in the existing mechanical space, and contribute to energy efficiency and redundant operation.

Replacing the old housed fan with a new one was quickly ruled out because it would have required extensive demolition and reconstruction and disrupted tenants. Instead, AEGON opted to replace the old fan with Fanwall Technology, a modular fan system introduced in 2004 by Huntair Inc., a CES Group company. The system’s multiple fans generate the 202,000 cfm required, but the modular design allows individual fan cubes to be navigated through the building and 3-ft doorways and stacked in place. The resulting system is more energy efficient and quieter than the existing huge fans, while also providing redundancy.

“We looked at Fanwall Technology as a way to upgrade the system without having to bring in a whole lot of demolition equipment,” said Dennis Latta, construction manager for the Pyramid Center. “It was a good option because we could redesign the layout of the cooling coils, fan intake, and ducting at the same time.”

At 853 ft high, with 48 stories and 500,000 sq ft of floor space, the Transamerica Pyramid requires multiple air-handling systems to serve the various zones of the building. Two mechanical rooms on the fifth floor serve two separate systems—a north side and south side—on floors 1 through 18. Each mechanical room has its own air-handling system, including fan, chilled water coils, and filters, and generates 101,000 cfm. The original fans in each mechanical room were the primary problem. About the size and weight of a Volkswagen Beetle, the housed squirrel-cage design posed an obstacle on several fronts, including demolition, replacement, and efficiency.

Besides the fans, each air handler dated to the early 1970s and had outlived its recommended life span. Some of the cooling coil drip pans were leaking, which posed potential corrosion problems and air quality issues. The likelihood of a catastrophic fan failure was high. Although spare fans and motors were available, delivery lead times were long. Replacing the fans and coils at the same time would save a considerable amount of labor and costs—but a like-for-like replacement of the fan would result in weeks of downtime, which was not an option in this busy facility.

Disruption, redundancy concerns

AEGON wanted to avoid disrupting tenants while keeping costs within budget. Installing a new housed fan would mean demolishing walls, expensive rigging costs to bring the fan in with a crane, plus long lead times and disruption to building comfort. In addition, the mechanical room was a small space, with little room for staging or equipment lay-down. The project would have spilled into the hallways, posing additional tenant disruptions.

Besides managing the logistics of the retrofit itself, additional goals were efficiency and redundancy. Gaining redundancy was important not only to ensure uninterrupted building comfort, but also because the fan system serves a 24/7 data center.

Fortunately, there was a simple solution that met all requirements. Shaun Webster, sales engineer with Norman Wright, the local manufacturers’ representative firm for Huntair, contacted Pyramid Center management to discuss technology as a viable solution.

Fanwall Technology provides multiple, direct-drive fans and motors in place of a single motor and fan. The multiple fans and motors provide redundancy in the event of a fan or motor failure because the remaining operating fans and motors continue to deliver airflow—and the smaller size and weight of the motors makes replacement easier.

In the Transamerica Pyramid building, multiple cubes of direct drive plenum fans arranged in a “wall” or bank replaced the large, forward-curved squirrel-cage fan in each of the two air-handling units in the fifth floor mechanical room. Each cube weighs about 600 lbs and includes a motor and fan. The entire system is custom-configured by selecting the number of fans, wheel diameter, and rpm to add up to the same cfm as the original fan. In the fifth floor mechanical room, two separate banks of 15 fans supply air and require less energy. Combined, they require 300 hp instead of the 400 hp required by the older system.

Space and time constraints

Two of the primary challenges for the demolition and construction were to maneuver and install the new fan system, coils, and associated piping in the confined space of the mechanical room, and to do the retrofit project in stages on weekends so tenants would not be inconvenienced.

“The design challenge I had was to find a space for the new fan system, upstream or downstream from the old fan, so we could get it all set up ahead of time, and then determine the geometry of the space,” said John A. Oldham, PE, principal of Oldham Engineering Inc., the mechanical firm for the project. Oldham Engineering had worked on other mechanical engineering projects in the building. “We had some difficult space to design in, and everything had to be measured ahead of time to the nearest inch—including height, width, conduit, pipes—so we knew everything would fit. We had the added advantage of being able to eliminate sound traps altogether, because the fans operate so quietly. That opened up another 5 ft on either side of the old fan.” The entire Fanwall system requires about 5 ft of space. That means all preparations could be completed while the old fan remained operational, virtually eliminating downtime for tenants.

Oldham had another goal: “To get more static pressure into the space and make the whole system run a lot better. The building has had overheating problems since it was built. Before we found Fanwall Technology, we couldn’t fix that. We couldn’t change out the fans because they were buried too deep in the building, and the building couldn’t be down as long as it would take to replace them. With Fanwall Technology, the ventilation conditions are a lot better, and we’re saving a lot of energy.”

The demolition and reconstruction work, completed in three weekends per side, was the responsibility of Kevin Frederick, project manager for the mechanical contractor firm Anderson, Rowe and Buckley Inc., San Francisco. Oldham had found enough space downstream from the original fan, and that’s where new construction occurred.

“Over the first weekend, we installed and commissioned the new coils, leaving the old fan in place with new coils,” said Frederick. On the second weekend, the old fan was removed, and Frederick’s team installed the new Fanwall cubes. The old fan measured 12 x 12 ft and included a 1900-lb motor and concrete base. Once the old fan was removed, “installing the Fanwall system itself was just a matter of getting the cubes in place, bolting them down, assembling and flashing off to the existing plenum and the new plenum area, and commissioning,” said Frederick.

On the third weekend, the existing coils and filter bank were removed and the new filter bank installed. The sequence was the same for the second mechanical room. The entire demolition and reconstruction was completed in six weekends, three weekends per side.

Less noise and vibration, reduced kWh

General contractor Randy Scott’s initial concerns about sound and vibration were abated soon after installation. “You can put your hand on the Fanwall system and there’s no vibration. You can have a normal conversation and hardly even know the fans are operating. That’s positive given that there are tenants on the floors above and below and a data center next door.” The reduced sound and vibration was also verified through an independent study commissioned by Huntair (see sidebar, Independent study highlights Fanwall system performance).

The operating characteristics of the Fanwall system have proven that it is more efficient than the single fan it replaced. The new system produces a uniform piston of air, creating a uniform velocity profile at the unit coils and filters and throughout the airway path in the unit. This uniform airflow profile reduces static pressure drop due to turbulence and system effects. As a result, the Fanwall system draws between 60 and 70 fewer amps than did the existing system. Transamerica Pyramid’s electrical consumption dropped by 80,000 kWh, or $25,000, during the first year of the system’s operation, earning the building a rebate incentive from Pacific Gas and Electric.

All of these factors are good news for Latta, whose focus as construction manager is energy savings. “The landlord, AEGON, has been supportive in a number of energy-saving projects. We’re an official green building now and want to keep that philosophy going forward. The new fan system supports that philosophy. It’s easy to see the difference between the fifth floor mechanical room and the other three mechanical rooms in the building. The fifth floor is quieter, more spacious, and the multiple array of fans makes it easy to understand why it’s unlikely we’ll have a major disruption to cooling on floors 1 through 18.”

Goals of replacement included using the same space, minimum disruption to tenants, lower maintenance, better efficiency, and redundancy.

Modular fan system using Fanwall Technology met all goals while allowing additional system changes to better improve performance.

Retrofit was completed on weekends with little or no interruption to normal operations.

Tenants and building management now benefit from a much quieter system, redundancy to avoid downtime, and a savings of 80,000 kWh in energy consumption.

Independent study highlights Fanwall system performance

Huntair commissioned Charles M. Saltar Assocs. Inc., to perform an independent study of the before and after acoustics and vibration characteristics of San Francisco’s Transamerica Pyramid replacement project.

Working with the building’s engineering team and equipment vendor, locations on the fifth (mechanical room) and sixth floors were chosen to represent locations typically occupied by tenants, engineers, and contractors. In multiple site visits during the removal of the supply fans and replacement with the Fanwall systems, noise and vibration levels were measured at various spaces. Additional acoustical measurements were conducted near the exterior louvers to estimate potential reductions in noise transfer to neighbors and exterior locations.

Measurements typically were taken in the very early morning, prior to the arrival of tenants, to reduce the potential for extraneous noise sources affecting measurements. Airflow rates, rotational speed, and drive frequency were monitored and programmed for the existing supply fans and the Fanwall systems to maintain consistency for acoustical measurement comparison.

Results from the study demonstrate that incorporating the Fanwall system reduced noise and vibration levels in the Transamerica Pyramid as follows:

At locations where supply air equipment dominated the noise environment, levels were reduced between 7 dBA and 13 dBA (8 dB and 17 dB overall) and 15 to 20 NC points. For reference purposes, a reduction of 10 dBA would be perceived as an approximate halving in loudness.

Vibration velocity levels at the building structure were reduced between 5 dB and 8 dB re 9.8 x 10-12 m/sec2.